The Dark Forest theory is fear-mongering anyway. If there's a civilization out there that wants to conquer others, it just has to send a probe to every star out there. Sufficiently advanced automation would allow this to happen without much work on their part. In theory, WE could do that right now, though very clumsily and with many failures. 3D printing, AI, harvesting materials off asteroids. Not outside of possibility, just hard at our level of tech. Now imagine the boogeyman of the Dark Forest theory - they would obviously have a greater level of tech if they're so dangerous, and it would be much easier.